Makefile: add missing references to DESTDIR

When cgit is built it needs to get CGIT_CONFIG and CGIT_CACHE_ROOT prefix
with DESTDIR.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

Makefile

@@ -31,9 +31,9 @@ VERSION: force-version
 CFLAGS += -g -Wall -Igit
 CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER)'
 CFLAGS += -DCGIT_VERSION='"$(CGIT_VERSION)"'
-CFLAGS += -DCGIT_CONFIG='"$(CGIT_CONFIG)"'
+CFLAGS += -DCGIT_CONFIG='"$(DESTDIR)$(CGIT_CONFIG)"'
 CFLAGS += -DCGIT_SCRIPT_NAME='"$(CGIT_SCRIPT_NAME)"'
-CFLAGS += -DCGIT_CACHE_ROOT='"$(CACHE_ROOT)"'
+CFLAGS += -DCGIT_CACHE_ROOT='"$(DESTDIR)$(CACHE_ROOT)"'
 
 
 cgit: cgit.c $(OBJECTS)